Presently known and used millimeter wavelength oscillators generally use high frequency oscillator elements as their main source of wavelength generation. These devices include such diode elements as the Gunn diode or IMPATT diode which oscillate in metal cavities. In the frequency ranges of interest, that is to say 35 GHz to about 300 GHz, there are applications for oscillators for use in communications and radar applications. These applications of such oscillator devices, it may be generally stated, involve the use of a low power output and low values of voltage bias for the control of the electronic portion of the oscillators used. The relatively high operating frequencies and related short wavelengths of the outputs require extremely precise construction of the oscillator physical components. The casting and machining for the parts of such devices and apparatus is extremely costly, which limits the practical applications wherein the use of such devices is economically feasible.
In order to benefit from the relatively high stability of the mechanically tuned diode units such as Gunn oscillators and IMPATT diode oscillators, because of their mechanical adjustment and setting features, it would be desireable to provide some ancillary type of adjustment which would not rely on a mechanical setting operation and which could fine tune the total oscillator structure without disturbing its basic mechanical setting or its mechanically set frequency in the resonating cavity.
This, then, was the state of the art when we conceived and developed our invention with the principal object of providing a fine tuning ancillary component combined with the basic mechanically tuned and set oscillator used in a cavity resonating device.
A further object of the invention is to provide an adjustably tunable millimeter wave energy source which has substantially rugged, inexpensive, and readily replaceable components.
A still further and important object of the invention is to provide the combination according to our concept and development with discrete and replaceable individual components being readily and commercially available without the need for specialized manufacture, fabrication, or assembly.
The invention, then, provides a compact, low cost, mechanically tunable Gunn oscillator with additional electronic tuning through the use of a coupled and operably assembled varactor diode which is completely housed in the same heat sink, chassis or oscillator structure in which the basic Gunn diode element reposes or is mounted. By changing the bias on the varactor diode through controllable electronic circuitry, the basic or set point range of the Gunn oscillator can be fine-tuned with hitherto unattainable precision and accuracy to frequencies within useful ranges on either side of the Gunn diode set point frequency.
The apparatus and system of our invention has found particularly advantageous utilization as an image line voltage controlled oscillator.